In the related art, a wiring board for mounting a semiconductor element such as an imaging element or an electronic component such as a crystal oscillator has a configuration in which wiring conductors made of metalized powder of tungsten, molybdenum, or the like are arranged on a surface of an insulating substrate made of electrical insulating materials such as an aluminum oxide sintered body.
Such a wiring board has decreased in size with demands in recent years for decreasing the thickness and size of an electronic device. Thus, in order to efficiently manufacture a plurality of wiring board, the wiring board is manufactured by dividing a many-up wiring substrate. The many-up wiring substrate has a configuration in which a plurality of wiring board regions serving as wiring boards are formed on an insulating base substrate in a matrix form.
In such a wiring board, a castellation conductor is often formed for connection with an external circuit board. In the related art, the castellation conductor has been formed by forming a through hole in an insulating base substrate for a many-up wiring substrate, arranging wiring conductors on side surfaces of the through holes to form a plating coating on the wiring conductors, and dividing the many-up wiring substrate along an intended cutting line that passes through the through holes in a plan view. Moreover, in order to secure a wide region for mounting electronic components on the wiring board, the castellations are often formed by dividing holes which are open on a main surface side that faces the mounting surface of the wiring board but are not penetrated. However, openings of castellation holes decrease as the size of the wiring board decreases and the number of pins increases in recent years. In the forming of a plating coating on the surfaces of the wiring conductors on the side surfaces of the castellation holes, since the opening of the hole is small, when the wiring conductor is immersed in a plating solution, gas remains inside the hole so that it is difficult for the plating solution to enter into the hole. Moreover, there is another problem in that even when the plating solution enters into the hole, it is difficult for the plating solution outside to circulate inside the hole. Further, when the plating coating is deposited by an electrolytic plating method, hydrogen is generated by electrolysis to produce bubbles, and the bubbles stay inside the hole so that it is difficult for the plating solution to enter into the hole. Due to this, it is difficult to form the plating coating to a predetermined thickness on the surface of the wiring conductors on the side surfaces of the hole, which causes a problem in bonding with an external circuit board or the like. In regard to such a problem, a technique is disclosed in which a dummy region is provided around an individual wiring board region, a through hole that penetrates from the dummy region side is formed on a bottom part of a castellation hole, and a through hole in which an opening of one main surface of the wiring board positioned close to the external circuit board is smaller than an opening of the other main surface so that the plating solution can easily circulate (for example, see Patent Literature 1).